1. Field of the Invention
This invention relates to waterborne reactive functional latex compositions containing pendant reactive functional groups which can undergo crosslinking. The reactive functional latex compositions are suitable for use in a variety of applications such as ultraviolet curing coatings; coatings with good wet-adhesion, block resistance and good tensile properties; as rheology modifiers, pigment binders, corrosion resistant coatings and the like.
2. Description of the Related Art
U.S. Pat. No. 5,268,417, discloses an aqueous dispersion of a copolymer obtained by free-radical polymerization and containing at least one aldehyde or keto group; the dispersion contains at least one polyisocyanate in which the isocynate groups are blocked with oxime. However, the dispersions of the reference present the disadvantage of emitting volatile organic compounds (VOC) upon deblocking of the isocyanate group.
U.S. Pat. No. 3,261,796 refers to modifying a carboxylic acid-containing latex with aziridine to produce amine groups on the polymer backbone. However, this reference exhibits the disadvantage of using toxic aziridine chemistry.
The publication by A. M. Schiller, et al, "Ionic Derivatives of Polyacrylamide", Industrial and Engineering Chemistry, 2132-2137, Vol 48 (1956), refers to a polyacrylamide made in an aqueous solution by free-radical polymerization which was subsequently transformed into sulfomethylated polyacrylamide in an aqueous solution. The reference further refers to a way of converting polyacrylamide into a cationic derivative or a polymer containing basic groups. This was achieved by reacting the aqueous solution of polyacrylamide with hypobromide or hypochloride and isolating the polymer by neutralization with HCl and subsequent precipitation by salting-out effect. The salting-out was facilitated by the presence of the large concentration of sodium carbonate and sodium chloride.
Kawaguchi, et al, Journal of Colloid and Interface Science, Vol. 97, 465-475 (1984), refers to a monodisperse styrene-acrylamide copolymer latex prepared by an emulsifier-free aqueous polymerization and subsequent modification of the latex to obtain a series of polymer latexes having the same particle size but different kinds and different amounts of functional groups on their surface. Thus, the amide groups were converted to COOH by hydrolysis, to OH-containing groups by reaction with HCHO, to NH.sub.2 by the Hofmann reaction, to NR.sub.2 by the Mannich reaction, and to SO.sub.3 -containing groups by the treatment with NaHSO.sub.3.
Tanaka et al, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 27, 4329-4339 (1989), refers to cationic polyacrylamides which contain both primary and quaternary amines, which were prepared according to a Hofmann reaction by adding choline chloride to a solution of polyacrylamide in water. The polymer solutions of the reference are used as flocculants. The polyacrylamide of the reference was synthesized by aqueous solution polymerization of acrylamide with potassium persulfate-isopropanol redox initiator. Sodium hypochloride solution was prepared by passing chlorine gas through a sodium hydroxide solution. The aqueous solution of the sodium hydrochloride prepared above was mixed with an aqueous solution of polyacrylamide to form primary and quaternary amines.
U.S. Pat. No. 5,539,073 to Taylor et al, refers to polymers useful in coating compositions, prepared by a free radical polymerization. The polymers of the reference possess pendant allylic groups which are capable of effecting free-radical flux when the compositions are applied to a substrate and exposed to oxygen.
The publication by R. W. Dexter, et al, "m-TMI, a novel unsaturated aliphatic isocyanate", Polymer Material Science and Engineering, 534-539, Vol. 53 (1985), refers to the use of .alpha.,.alpha.-dimethyl-meta-isopropanol benzyl isocyanate (m-TMI available from American Cyanamid Company). The incorporation of the pendant functionality is accomplished by reaction of m-TMI via copolymerization to introduce pendant aliphatic isocyanate, or via post-reaction of m-TMI with a polymer containing hydroxyl, --NH or --SH groups on the backbone to introduce pendant unsaturation on the backbone of the polymer. The authors indicate that this material has the ability to undergo copolymerization in aqueous emulsion systems with minimal hydrolysis of the isocyanate functionality. The low reactivity of this highly hindered isocyanate is also discussed. However, m-TMI is an expensive monomer.
Thus, there exists a need for waterborne latex compositions having pendant reactive functional groups. The functional latexes should be able to enhance properties of the latex without requiring the use of blocked isocyanates that need to be deblocked in a separate step after latex synthesis; not require the use of crosslinking chemistry that results in the release of protective groups that create environmentally undesirable or toxic volatile organic compounds (VOC) such as formaldehyde or methanol; and not require excessive high heating or addition of acid or heavy metal catalysts. Further, there exists a need for low temperature or ultraviolet light (UV) crosslinkable latexes having the crosslinking functionality on the surface of the latex particles rather than randomly distributed throughout the latex particles and not readily available for crosslinking. There is also a need for methods to introduce reactive functionality onto latex particles subsequent to particle formation, especially functional groups that cannot remain unreactive during latex polymerization.
It is an object of the present invention to provide waterborne latex compositions having pendant reactive functional groups. The latex compositions are suitable for coatings applications; do not generate undesirable VOC side products; and contain low levels of amide functionality.
It is another object of the present invention to provide crosslinkable waterborne latex compositions exhibiting superior tensile properties and chemical resistance properties.
It is a further object of the present invention to provide methods for preparing waterborne latex polymers having pendant reactive functional groups.